Overhaul `RefPtr` and `String`

- `RefPtr` no longer tries to have distinct cases for interal-vs-external reference counts. Instead we always require an internal reference count.

  - Types the used `RefPtr` but weren't `RefObject` were made to inherit `RefObject`

  - The `ReferenceCounted` base class was removed, so that only `RefObject` remains

  - Implicit conversion from `RefPtr<T>` to `T*` added
    - This created some complicates for other types that relied on implicit conversions, so this isn't a net cleanup right now

- The main type that got messed up by the above was `String`, which previously held a `RefPtr<char, ...>`. This change thus *also* includes a major overhaul of `String`:

  - `String` now holds all its data via indirection, using a `StringRepresentation` that is a `RefObject`. This object holds a length, capacity, and directly stores the character data in its allocation. This means that `sizeof(String)==sizeof(void*)`

  - It is now possible to directly mutate a `String` by appending to its representation (we just need to ensure it has a reference count of `1`, possibly by cloning it). This means that `StringBuilder` is now basically just an idomatic use of `String`

  - A couple operations that just return sub-ranges of a `String` now return `StringSlice` to avoid allocation when it isn't needed. This required more work.

  - Indices into strings changed from `int` to `UInt` (which is pointer-sized). This had a bunch of follow-on changes because the value `-1` sometimes needs to be special-cased in code that uses indices. Further cleanups are probably needed here.

1 files changed, 2 insertions, 2 deletions

diff --git a/source/slang/parameter-binding.cpp b/source/slang/parameter-binding.cpp
index 01b047c2c..2a0c64892 100644
--- a/source/slang/parameter-binding.cpp
+++ b/source/slang/parameter-binding.cpp
@@ -211,8 +211,8 @@ LayoutSemanticInfo ExtractLayoutSemanticInfo(
     // TODO: need to parse and handle `space` binding
     int space = 0;
 
-    int index = 0;
-    for (int ii = 1; ii < registerName.Length(); ++ii)
+    UInt index = 0;
+    for (UInt ii = 1; ii < registerName.Length(); ++ii)
     {
         int c = registerName[ii];
         if (c >= '0' && c <= '9')